Copolymers of styrene and alphamethyl styrene and process for making the same



poisesat 2'5? Patented May 12, 1953 UNI-TED .s1-Ares PATENT- oi-Fic i,

CPLYMERSOF l METHYLSTYRENE ANpPRooEssf FR- MAK-ING- THE SAME James Ware riginalappiiooiion kJanuary 3, 19'5'0; serial o;

13625871.1' Divif'lfed-y and this application August 20, 1952; Sil N. 305,444.

2 Claimsi' (Cl. U-SU 1 This applicationi's 1 adivision of our eopendin'g application', SerialvNo; 11365584g-l`ed January 3, 1950."

This inventionooncerns-janimproved process for making'- solid copolymers of 'styreneand' alpllal-iiiethyl1l 'styrene which opolfyrnersipossess greater dimensiona'llstabixlity tofheat; e; withstand 'higherte'mperatures Witl'routv loeconiii-'ig n distiallycompletedyby heating the mixturevto a higheritemperaturewhich forms a copolymer of the renlaini'ngA monomers I'having an absolute 'viscoityinf tolueneoffabout 15 centipoises, or

less-,fatf25f C; a

It has also beenlnoted that the formation-of the non-Volatile methanol solublesubstancesoctorted;thanfpolystyrenewhich has' been# prepared l undery similar polymerii'iationconditions: It i 'relatesmore particularly to v solid' 1 copolymers' of styrene -and alpha-Inethy-l styrene whichV are characterized yby: having a-"high'er hea-tf distortion temperaturefthaii polystyrene offs'imilar' 'moleoular Weightand AWliiclfi -eontain-fless than one per cent--by Weight 'ofT methanol soluble substances.-A

It is known `toY prepare' thermoplastic` resinsV by polymerzing styrene withl alpha-methyl styrene and to recover the copolymer produce inpuried form 'by' distilling unreacted monomers -to'- gether With""otl1er' volatile'-V ii'igredietsy-e. g. dimers'or trimersothe monomeric compounds.

We have observed-"that 'tlie' Acopolymers Ioi" styrene and alpha-*methyl `etyrene` vary Widely in properties 'suchL as Adimeirsional'stabilityto "heat, tensile" strengtli;impact', or per cent' solble'in methyl alcohol; depending' in part 'upon the polymerizing conditions,v Le'. the manner in which' `the polymerizationjf reaction is cai-led' out; and alsov uponfthe conditionsv of 'temperature and time to which `'the 'copolymer is"r` subjected during purification of' the" same byfdistillirlg' off Volatile ingredients; K

The' copolymers 'of' styrene'and lalp'liait-i'iil'ei-.liyl styrene prepared by polymerization"`metlfiods usually employedtovpolymerize' styrene'g'efg. by

polymerization iiibulk,` frequently c'ontaiofrom 2 to 5.peif' cent by'weight, or moreg'ofsubs'tancfes formed as hyp-products" of the v'polymeri'zal'ion reaction, which' byepr'oduct substances" are soluble in` methanol; but cannot' readily beA separated vaporizing in vacuum.L y

It has beenl obs'ervedthatltl'ie formation "of the. non-volatile nle'tlsianl` soluble fsiibfstalces usually occurslwhe'n. a mixtur'f' styrene' ar'id `al hal-methyl styrene. is v.polymerizellin hul by heating, line same io, a. .polymerization iiofiipeiature/such thatj the copolymer obtained" forms) a 10! Weight per cent solution intoluen hai/ing" an absolute viscosity of, less ithan'fiabout-fl5` centi- C.L The non-ivolatile m'thanlfsol- .ble substances are also formed when the' mlxtu'e L of. polymerizable starting" materialsis polymerizd to'. 8'0"-.9oper cent completion 'at a'fteniperature s'uch that'tlie copolymerjtliusproducoc"formsja ro` weight upor centisoiiiftiion t'oliieire7 having an the polymerization isfinshed off, ory substancurs Wlien'af:.so1id'=high copolymer of styrene and aloba-'methyl` 'sty-rene is heated at Atemperatures above'fitsmelti-ng point for prolonged periods of tilrie; particularly rat; temperatures suchV as are requiredV tof rapidly'rvaporize fvolatileingredients therefrom in,vacuum-.1:.`

The non-volatile methanolisol'uble by'product substances #are believed toben composed' principallyfoof polymerseor copolymers of relatively 10W molecular Weight. Regardless'of the composition'iori the nnevolatile methanol soluble subst'arfloesgfthe presencev ofmore" thanabout one lpeli" centfby .weigh-tiof such methanolI soluble byproduct' substance'siri admixture With the copolymer loifersl' 'the 'hei-ttf'l distortion temperature 'of the copolymer lby an 'undesirableamount y Such polymerica-produotsioflalphamethyl styrene and styrene'- usually!possess-inferior properties, partieularly` WthI-reg'ardto dimensionalistability to heat: Y

It is therefore :apri-)mary object oftheA invention iersio styrene and alpha'eii'lethyl styrenel which copolymers possess greater dimensienal stability to heat tllariplystyrerre 'off similar :molecular Weight. "Another'ob-jectis to'. prepare copolymers of 'styrene and":lpliaemethyl-Styrene which copolymersV can readily be moldedlinvusual ways to form'v articles" havirigif'diriesional v"stability at 'temperatures feorrespond-ing tothe atmospheric boiling--poiritof' Water. further object' is to prepare copolymersL off-styrene and alpha-methyl y'tive polymerization reaction A stilly further objeoti's' ioprovidef-a process for making improved copolymers ofv Vstyrene and lalpin-foeiiiyi 'thereafter' separating volatile -i'rig'redik'enl's'r` from `the. copolymer by*I piroceidurief'which1 avoids' decomposition-or the 'copoiyiiraf`- to iorimnoiivolatile methanol' sol'ubl' 'sub'stancesi Other and related objects willy become apparent'from the roll-owine description of the inyeatioiifi copolymer" of ene whicllif; are

superior to polystyrene, particularly asa regards dir'l'eso'lial stabiltyto'heatican bepreparedby procedure which involves heating a mixture of ,togetherv with other volatile v `vaporized while the copolymer is mechanically, worked or agitated in vacuum by a kneading or the polymerizable materials in bulk, i. e. in the substantial absence of inert liquid media, to a temperature below that at which methanol soluble substances are formed, and thereafter vaporizing volatile ingredients from the product by heating the latter under vacuum to a temperature above the melting point of the copolymer, for a time less than is required to cause decom- 4 lar form is obtained. In the system, a mixture of styrene l and alpha-methyl styrene 5, in the desired proportions, is polymerized to form a solid log or billet -of a size suitable for convenient handling. Such billets may be obtained 'by sealing the mixture of monomers in a sheet position of the same at the temperature employed, removing the vapors from contact with the copolymer and cooling the devolatilized copolymer,

The invention may be further explained With reference to the accompanying ldrawing, in which Fig. 1 is a flow diagram illustrating a procedure for the production of a copolymer of styrene and alpha-methyl styrene in continuous manner by polymerizing a mixture of the monomers to obtain a fluid solutionof the copolymer in monomers, e. g. a solution containing 30 per cent by weight or more of copolymer, and thereafter separating the volatile ingredients from the copolymer;

Fig. 2 is a ow diagram illustrating a procedure for production of the copolymer by maintaining a mixture of styrene and alpha-methyl styrene in bulk at a polymerization temperature until nearly all of the monomers are polymerized, i. e. until a solid resin is obtained, and thereafter devolatilizing the copolymer, and

Fig. 3 is a similar diagram illustrating another method of separating the volatile ingredients from the copolymer.

In the procedure of Fig. 1, the styrene 4 and the alpha-methyl styrene 5 are charged in the desired proportions into a mixer 6, such as a- -tank provided with a propeller agitator and stirred together to produce a uniform liquid mixture. The mixture of monomers is fed in continuous manner -by a metering pump I into a polymerizer 8 closed vesselv provided with heating or cooling coils, a stirrer and suitable inlets and outlets for feed of the monomersthereto and discharge of -the copolymer solution. The copolymer solution is withdrawn from the polymerizer 8 by a metering pump 9 and is fed into a heated vacuum de- :volatilizer and extruder I0, adapted for continuously forwarding and discharge of the codpolymer .by extrusion while separating volatile ingredients therefrom.

In the devolatilizing system I0, which is main- I .tained at a temperature at which the polymeric product is freely nuid, the unreacted monomers ingredients are stirring action to provide a changing surface for l escape of thevolatileingredients from the fluid copolymer. y forced through an extrusion orifice and is drawnv away and cooled to solid form. Vapors of the The devolatilized copolymer is then unreacted monomers ltogether with other volatile ingredients are separately withdrawn from the system I through a suitable outlet connected to a vacuum pump, with a recovery unit therebetween for condensing liquid substances. An apparatus suitable for use as the devolatilizer and extruder I0 is described in U. S. Patent 2,488,189.

The procedure of Fig. 2 is useful in separating volatile ingredients from the copolymer, when a mixture of styrene and alpha-methyl styrene is polymerized in bulk until a solid resin which can be ground or crushed to a non-tacky granuwhich may conveniently be a.

metal container, e. g. a tin lined or 10 gallon sheet metal can, and submerging the can in a liquid bath or batch polymerizer II, maintained atal desired polymerization temperature. The polymerization reaction is continued until nearly vall of the monomers are polymerized, i. e. until 95 per cent or more of the monomers are polymerized. Thereafter, the can is stripped from the solid resin and the latter is ground or crushed to a granular form by a suitable grinder I2. The granular polymeric product is then fed into a heated vacuum devolatilizer and extruder I0 and the volatile ingredients separated from the copolymer as heretofore described.

The procedure of Fig. 3 illustrates another method of separating volatile ingredients from the copolymer whenv the polymeric product is obtained in solid form. In the system, the polymerization and grinding of the solid polymeric product to a granular form are accomplished by procedure similar to that described with reference to Fig. 2. The granular polymeric product is fed into a suitable heater and extruder I3, where it is rapidly heated to a temperature above its melting point,l e. g. a' temperature of from 200 to 280 C., preferably to a temperature between 240 and 280 C. The heat-luidized polymeric product is fed by pressure of the extruder into an upper portion of a vacuum chamber devolatilizer I4, wherein it is formed into thin streams, or strands, which are permitted to flow, or fall, for a material distance out of contact with inner walls of said chamber through a zone of reduced pressure to vaporize volatile ingredients from the copolymer. The strands of fluid plastic coalesce to form a uid mass of copolymer in a lower portion of the chamber I4. The copolymer is withdrawn from chamber I4 by metering pump I5 and cooled to solid form. Vapors of the volatile ingredients are separately withdrawn from the vacuum chamber through an outlet connected to a suitable vacuum pump, not

is employed in amounts corresponding to from 15 to 40 'per cent .by weight of the combined weight of the polymerizable starting materials.

It is important that the mixture of styrene and alpha-methyl styrene be polymerized under temperature conditions which avoid, or at least restrict greatly, the tendency toward the formation of non-volatile methanol soluble substances. In this connection, the mixture of monomers Eshould be polymerized at 'a temperature not greater than that required to form Ia normally solid copolymer having an average molecular weight such that :a solution consisting of 10 per cent by weight of the copolymer in toluene has an absolute viscosity of at least 18 at 25 C. The

approximate maximum polymerization temperature to be employed for any mixture of styrene factory. The shape of the passageways is immaterial, provided the melted copolymer is formed into streams which have a large surface compared to volume. In general, circular perforations, or drill holes having a diameter of 1/8 to 1/4 inch are preferred. Slots having a width of 11g to 1A; inch represent about the range which can be used practically. The stream, band, or ribbon, of heated copolymer formed by passing the meltedpolymeric product through a die plate into a ,vacuum chamber is permitted to flow, or fall, therein for a material distance, e. g. for a distance of from 2 to 6 feet or more,-out of contact with inner walls of said chamber so as to expose the heated copolymer to vacuum for a time sufficient to vaporize the volatile ingredientsand leave a copolymer residue, or product, containing less than 1 per cent by weight of methanol soluble substances.

Other ways of separating the lvolatile ingredients from the copolymer product will be apparent to those skilled in the art. However, in all such devolatilizing procedures the copolymer should not be heated at temperatures above its melting point for periods of time sulicient to cause the formation of decomposition products which lower the heat distortion temperature of the copolymer.

The copolymers of the invention are normally solid polymeric products which may be dissolved to form weight per cent solutions in toluene having absolute viscosities of 18 centipoises, or greater, at 25 C. The copolymers can be molded by conventional methods in compression molding, or injection molding apparatus, to form articles having dimensional stability to heat 'superior to articles made from polystyrene of similar molecular weight. The copolymers contain less than 1 per cent by weight of methanol soluble substances. They may be molded to form transparent colorless articles having excellent electrical properties, and good tensile and impact strength.

The following examples illustrate ways in which the principle of the invention has been applied, but are not to be construed as limiting the invention.

EXAIVDPLEl In each of a series of experiments, a mixture of styrene and alpha-methyl styrene in the proportions indicated in the following table, together with 0.01 per cent of di-tertiary-butyl peroxide as polymerization catalyst, was polymerized by heating the same in a closed container in accordance with the schedule of time and temperature conditions stated in the table. The polymeric product was removed from the container and heated to a temperature of 190 C., at an absolute pressure' of from 1-2 millimeters 'of Hg, over a period of 2 hours to remove volatile ingredients. Thereafter, the copolymer from each of the experiments was cooled to room temperature and the solid resin crushed to form granules of a size suitable for molding. A portion of each of the copolymers was injection molded to form test bars of 1/8 by 1A; inch square cross section. The test bars were used to determine the tensile strength in pounds per square inch of initial cross section and the impact strength of each product in inch-pounds of energy, applied as a sharp blow to `cause breakage of a test bar. Except for the shape and dimensions of the test bars and the Weight of the hammer used in measuring impact strength, the procedures in determining strength and impact strength were similar to those described in A. S. T. M. D638-44T and A. S. T. M. D256-43T, respectively. Other molded pieces were used to determine the heat distortion temperatures by a procedure of Heirholzer and Boyer, A. S. T. M. Bulletin No. 134 of May 1945. Other portions of each copolymer were tested to determine the proportion of residual volatile material therein, the proportion of methanol soluble substances therein, and a viscosity characteristic of the copolymer. The procedure in determining the proportion of residual volatile material was to weigh a portion of the granular copolymer, then heat it to a temperature of 216 C. at an absolute pressure of 0.05 millimeter of Hg over a period of 30 minutes and cool and re-weigh. The loss in weight represents volatile ingredients. The procedure to determine the proportion of methanol soluble material was to dissolve a weighed amount of the copolymer in dioxane, precipitate the polymer in methanol, separate and dry the precipitated polymer and determine its weight. The loss in weight represents methanol soluble material. It should be noted that the per cent methanol soluble material also includes the residual volatile materials. The viscosity characteristic was determined by dissolving a portion of the copolymer in toluene to form a solution containing 10 per cent by weight of said product and determining the absolute viscosity in centipoises at 25 C., of the solution. Table I identifies each copolymer by giving the per cent by weight of styrene and alpha-methyl styrene in the mixture polymerized, the conditions of time and temperature at which the polymerization was carried out, the per cent methanol soluble material in the copolymer and the viscosity characteristic. The table also gives the properties determined for each product. For purpose of comparison copolymers prepared under polymerizing conditions outside the scope of the invention are also included in the table.

Table I P t Polmileizzlition ercen fe u e l i V Percent Percent Heat Dis- Impact Tensile Run No. ggl gs Polymeri- CHsOH Vlsglty tortion Strength, Strength, styrene Time, Temp zation Soluble Temp., C. inch-lbs. lbs./sq. in.

days C. l l l5 85 20 10.2 99. 1 0. 20 0. 98 59. 4 89 l. 4 9, 660 15 85 10 110 98. 8 0. 40 0. 89 42. 1 90 1. 5 8, 760 l5 85 6 120 98. 8 0. 26 0. 93 25. 2 91 1. 3 8, 690 15 85 3 130 98. 8 0. 23 O. 92 18. 1 88 0. 9 8, 420 25 75 20 102 98. 0 0. 08 0. 72 38. 2 97 l. 0 9, 380 25 75 l() 110 97. 7 0. 3l) 0. 67 30.1 96 0. 9 9, 540 25 75 li 120 97. 5 0. 27 O. 82 18. 5 93 l). 7 8, 190 25 75 3 130 90. 7 0. 19 l. 27 13. l 88 0. 6 7, 630 50 50 20 102 .85. 1 0. 20 0. 79 19. 2 107 0. 7 8, 650 v50 50 10 llO 8l. 2 O. 25 l. 15 12. 3 101 0. 7 7, 620 50 50 6 120 80. 5 0. 49 2.16 9. 7 101 0. 5 7, 260 50 50 3 130 78. 5 0. G5 2. 70 7. 8 98 0. 5 4, 650

show a substantial-lowering of the lheat distor- -tionitemperature as wellfas--a large decrease in the vtensile strength. .as compared' to the copoly- 'mers'within thescope of the invention.

EXAlWPLE 2 In each of'aV series of experiments, Ya mixture -of'styrene and alpha-methyl styrene in the proportions indicated. in thef'following ltable, was 'poly'merized by heat-ing thesame in a closed-container in 'accordance vWith the schedule "of time 'and temperature conditions stated'in the table. nach mixture was 'polymerized under conditions s'uoh as 'to obtain copolymers having approximately thesame ancrage'l molecularweig'litas determined by the viscosity characteristic-of la Weightv` per centv solution of the copolymer in toluene at C. 'The polymeric product' was removed from the container and heated in vacuum to a temperature of 150 atan vabsolute pressure of "from 1--2 millimeters of Hg, overnaperiod of '2" hours to separate Volatile ingredients. The-copolymers were then cooled and crushed to a' size suitable for molding- Thereafter, the vis- 'cosity characteristics, the per cent volatile, and the per-cent methanol soluble materialof'the yc'opolyniersA and :also the impact strength'iand the heat distortion -temperature of testl bars Vr'nold'ed from thesame,v 4weredetermined as in Example `1.-' Table I'identi-eseach polymer by 'naming the monomeric materials from -vvhich it.

was-prepared and gives the 'properties determined for eacheproduct. For comparison, styrenel and va'crsiilyrn'e'r-outside the scope of the invention are vincluded in the table 4as'runs 1 and 8; respectively.

10 40G-.pounds per-hour into a screw. .feeder .wherein itwas melted and rapidly heated toa temperature of 275 C. The fluid polymericproductwas caused to riiovv by pressurefrom the screw feeder via a jacketed and heated. conduit through a distributor head24 inches in diameter having approximately. 2,000 perorations, consistingof 1A; .inch drill holes yons/4A inch centers, into the top of 4a jacketed vessel 9 feethigh `having an internal diameter .of 27I inches, wherein the thin streams 'ofi hot resinous material were permitted to 110W .freely out of contact with inner Walls of the vessel v.throughout a greater part of the interior length vof the vessel while being subjected to highlvacuum, i. .e. an absolute pressure of from 3 4 millimeters or Hg, tovaporize volatile ingredients from the-copolymer. Vapors of the volatile ingredients Were removed from the vacuum chamber Via an outlet in tha-upper portion thereof, connected to a condenser and a vacuum pump. The Ystreams of devolatilized polymericproduct ycoalescedy or flowedrtogether, to iorrn a viscous liuid mass of the puriiied` copolymer product Within alower portion of the vessel. The devola- -tilized copolymer was removed from the vacuum chamber by means of a plastic gear pump Aoonnectedto4 'an-opening in the bottom of the vessel. The pump also served as a valve` or seal so that the copolymer could be Withdrawn .Y intermittently, orin continuousmanner, from the-vessel. The .devolatilized copolymer Was fed at a temperature of about 265 C., via aiconduit, from the pump, onto Water cooled rolls and Was-compressed therebetween` into a thin sheet and rapidly cooled to a temperature ofapproximately C., then ground totorm a granular powder. The inventory time, i. e; the time interval between feeding anvini-lnitesimal.portion 'of the Asolid granular" polymerization vproductl rinto the Percent Percent Heat; Dis- AImpact Rim Pefent Alpha' Polymere irlt Hson SC05/1W tortion strength, No stylen@ -methyl ration @lame Soluble cps' Temp C in -lbs Styrene Time Tfpq l0() 0 4 hrs 130 77 0.33 50 85 1.0 90 l0 l5 hrs. l2() 87 O. 29 44 89 0. 9 80 $20 35 hrs.. 111 73 0. 46 42 95 l. l '30 4 days..- 102 75 0.33 47 97 1.4 l6u 4o 1.o.5 days-. 93 70 0. 43 49 101 1. 2 5 0 5U 25 days 83 54 0. 40 48 104 1.2 25 4 days '.102 59 0.49 45 94 4 days. 102 75 25 2 days ll() 98 0. 85 49 86 2 days... r240 ...EXAMPLE 3 A mixture consisting of 17,250 ypounds of styrene and '5,750 pounds" of `alpha-n'iethyl styrene,

together With 2.3 pounds :of di-'tertiaryebutyl peroxide as 'polymerization catalyst', Wassealed in a number of 'closed sheet metal 'containers,'each containing approximately 90 pounds of the mixture. The mixture Was polymerized by submerging the containers in a liquid bath and heating vthe latter according .to the following schedule of time and temperature conditions: 2 .days at a temperature of '88 C.; 2 days at 83 C.; 3days at C'.'; 3 days at .84 C.; 1 day at 87 0:; 2 days at C.; 2 Vdays at 95 C.; and 2 days at 150` C. Thereafter, the containers Wereremoved from the bath, cooled to room' temperature and the `polymeric product removed from the container and crushed -to a granular form. The'. solid .granular polymeric product was fed a't arate of screw feeder and cooling the infinitesimal portion of thedevolatilized copolymer on the rolls,--was about 8 minutes. Samples of the devolatilized granularcopolymer were 'Withdrawn at-intervals and the properties determined asin Example 1.

- EXAMPLE -4 A mixture consisting of 20 per cent -by1weight alpha-'methylfstyrene and 80 per cent styrene was fed. in continuous manner into a `jaciieted Vessel equipped with valved inlets, a steam coil and. a stirrer, wherein the mixture was Vpolymerized by heating the same to-a temperature of C., while stirring, until a solution-containing vabout 50 per cent by weight of copolymer was obtained. Thereafter, the mixture of monomers was fed into the vessel at a rate of 12 pounds per hour while a solution containing approximately 50 percent by weight of copolymer was withdrawn from a lower portion of the Vessel at a rate corresponding to the rate of feed thereto. The solution of copolymer in monomers was fed by means of a plastic gear pump into a zone maintained at an absolute pressure of 25 millimeters of Hg, wherein the solution of copolymer was contacted with heated surfaces of a roll, adapted for continuously forwarding and discharge of the copolymer by extrusion by rotating adjacent to heated walls of a complementary casing with suitable clearance for flow of the plastic therebetween and escape of the vaporized Volatile ingredients to a chamber connected to a vacuum pump. Sufficient heat was supplied to the copolymer through surfaces in contact therewitln to Vaporize the volatile ingredients and. maintain the copolymer in a fluid condition. The copolymer was extruded from the zone of reduced pressure at a temperature of 235 C., through a constricted passageway at a rate of about 6-" pounds per hour and was drawn away and cooled at a solid form. The inventory time was approximately 60 minutes. Properties of the copolymer were determined as in Example l. The

copolymer had a heat distortion temperature of 91 C. and contained 1.09 per cent by weight of methanol soluble substances. A solution consisting of 10 weight per cent of the copolymer in toluene had an absolute viscosity of 35 centipoises at C.

EXAMPLE 5 A purpose of this experiment is to illustrate the tendency toward the formation of nonvolatile methanol soluble substances and de- Vapors of volatile ingredients were removed from the Vessel through an outlet in an upper portion thereof connected to a condenser and vacuum pump. The streams of devolatilized'copolymer coalesced, or flowed together, to form a viscous fluid mass of the same within a lower portion of the vessel. The uid copolymer was withdrawn from the vacuum chamber by means of a plastic gear pump connected to an outlet in the bottom of the Vessel and was rapidly cooled to a solid form. The pump also served as a seal so that the copolymer could be withdrawn intermittently, or in continuous manner, from the vacuum chamber. The inventory time, i. e. the time interval for an innitesimal portion of the granular polymerizationy product fed into the screw feeder to traverse the system and be cooled to a solid, was approximately l0 minutes when the copolymer was withdrawn from the vacuum chamber at a rate substantially the same as the rate of feed thereto,. which rate was about 7 pounds per hour. In an experiment to determine the effect of prolonged heating at high temperatures on the devolatilized copolymer, a body of the devolatilized product was allowed to accumulate in the vacuum chamber over a period of 2 hours, where it was maintained at a temperature of about 270 C. Thereafter, the feed was stopped and the chamber lled with nitrogen gas at a pressure of 10 pounds per square inch, gauge. After storing for a time of 1 hour under nitrogen, approximately one-third of the copolymer was withdrawn, rapidly cooled to a solid and crushed to a granular form. The remaining copolymer was withdrawn from the vacuum chamber in two portions after storing under nitrogen at a temperature of 270 C. for 6 hours, and 16 hours, respectively. The viscosity characteristic, the per cent volatile, and the per cent methanol soluble of the different portions of copolymer and also the heat distortion temperature of test bars molded from the same, were determined as in Example 1. Table III identifies each portion of the copolymer by stating the total time for which it was heated and also gives the properties determined for each product.

presence of 0.01 per cent of di-tertiary-butyl perand heated Vessel 42 inches high having an internal diameter of 6 inches. The thin streams of hot resinous material were permitted to ow freely out of contact with inner walls of the vessel for a distance of about 36 inches into a lower portion of the vessel while maintaining an absolute pressure of 3 millimeters of Hg therein.

Other modes of applying the principle of the invention may be employed instead of those explained, change being made as regards the compounds or steps herein employed provided the compounds or steps stated in any of the following claims, or the equivalent of such compounds or steps be employed.

We claim:

l. A process for making a copolymer of styrene and alpha-methyl styrene which comprises heating a mixture consisting of from 10 to 50 per cent by weight of alpha-methyl styrene and from 90 to 50 per cent of styrene to a polymerization temperature between C. and a temperature dened by the equation:

wherein t represents temperature in degrees centigrade and :r is the per cent by weight'of alpha-methyl styrene in the polymerizable starting materials, until a solid polymeric product is obtained, the said polymeric product comprising a copolymer of styrene and alpha-methyl styrene having an average molecular weight such that a weight per cent solution of the copolymer in toluene has an absolute viscosity of at least 18 centipoises at 25 C., comminuting the solid polymeric product, heating the granular polymeric product to a ytemperature between 240 and 280 C. over a period of time of less than 60 minutes while feeding the heated polymeric product into and from a zone of reduced pressure wherein it is formed into thin streams which are subjected to an absolute pressure of less than 25 millimeters to vaporize volatile ingredients and leave a copolymer residue containing less than 1 per cent of methanol lsoluble substances, separately withdrawing vapors of the volatile ingredients and the heat-plastied copolymer from the zone of reduced pressure `and cooling the copolymer.

2. A process for making a copolymer of styrene and alpha-methyl styrene which comprises polymerizing a mixture consisting of from 10 to 50 per cent by weight of alpha-methyl styrene and from 90 to 50 per cent of styrene by heating the same to a temperature between '70 C. and a temperature dened by the equation:

wherein t represents temperature in degrees centigrade and .1.' is the per cent by weight of Valpha-methyl styrene in the polymerizable starting materials, until a solid resin is obtained, the said resin comprising a copolymer of styrene and alpha-methyl styrene having an average molecular weight such lthat a 10 weight per cent solution of the copolymer in toluene has an absolute viscosity of at least 18 centipoises at 25 C., heating the polymeric product to a temperature between 240 and 280 C. over a period of time not greater than minutes while feeding the heated polymeric product into and from a zone of reduced pressure wherein the heat-uidized resin is fed through a number of constricted passageways as thin streams into the upper portion of a vacuum chamber maintained at an absolute pressure of less than 25 millimeters of Hg and is allowed to ow out of contact with inner walls of the chamber into a lower portion of said chamber while vaporizing volatile ingredients therefrom so as to leave a copolymer residue containing less than 1 per cent of methanol soluble substances, separately withdrawing vapors of the volatile ingredients and the heatfluidized copolymer from lthe vacuum chamber and cooling the copolymer.

JAMES L. AMOS. CARROLL T. MILLER.

No references cited. 

1. A PROCESS FOR MAKING A COPOLYMER OF STYRENE AND ALPHA-METHYL STYRENE WHICH COMPRISES HEATING A MIXTURE CONSISTING OF FROM 10 TO 50 PER CENT BY WEIGHT OF ALPHA-METHYL STYRENE AND FROM 90 TO 50 PER CENT OF STYRENE TO A POLYMERIZATION TEMPERATURE BETWEEN 70*C. AND A TEMPERATURE DEFINED BY THE EQUATION: 